I just launched a Bitnami OpenCart on Google Cloud Platform and I can confirm that the next configuration files and binaries exists:

/etc/vsftpd.conf
/usr/sbin/vsftpd
/usr/bin/sftp

On the other hand you don't need to edit the file /etc/vsftpd.conf file in order to configure FTP on OpenCart. The steps to do so are:

Set a password for the bitnamiftp user if not already set. Connect to your server using SSH and run the commands below to set this password:

sudo passwd bitnamiftp

Restart the vsftpd server:

sudo service vsftpd restart

Configure the FTP settings in OpenCart. Navigate to the "Settings" page, click the "Edit" button and select the "FTP" settings. Configure using the data below, remembering to replace the PASSWORD placeholder with the correct password for the bitnamiftp user.